From c79fb6b7965b4e10faba97e715c1ccb016c1f64a Mon Sep 17 00:00:00 2001
From: Mats Palmgren <matspal@gmail.com>
Date: Mon, 5 Nov 2012 23:43:44 +0100
Subject: [PATCH] Bug 807174 - Drop-down list used inside a frameset document
 renders outside the frame.  r=roc a=lsblakk

---
 layout/forms/nsComboboxControlFrame.cpp | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/layout/forms/nsComboboxControlFrame.cpp b/layout/forms/nsComboboxControlFrame.cpp
index f5e216503aa..9f7197fd949 100644
--- a/layout/forms/nsComboboxControlFrame.cpp
+++ b/layout/forms/nsComboboxControlFrame.cpp
@@ -653,11 +653,12 @@ nsComboboxControlFrame::GetAvailableDropdownSpace(nscoord* aAbove,
   }
 
   nscoord minY;
-  if (!PresContext()->IsChrome()) {
-    nsIFrame* root = PresContext()->PresShell()->GetRootFrame();
+  nsPresContext* pc = PresContext()->GetToplevelContentDocumentPresContext();
+  nsIFrame* root = pc ? pc->PresShell()->GetRootFrame() : nullptr;
+  if (root) {
     minY = root->GetScreenRectInAppUnits().y;
-    if (mLastDropDownBelowScreenY < root->GetScreenRectInAppUnits().y) {
-      // Don't allow the drop-down to be placed above the top of the root frame.
+    if (mLastDropDownBelowScreenY < minY) {
+      // Don't allow the drop-down to be placed above the content area.
       return;
     }
   } else {